Java split（）无法按预期工作

Question

I currently have text where I have "TweetJSONObject\\r\\n09/19/14TweetJSONObject" where the TweetJSONObject is just a tweet in json format. Now I'm using the .split() function to try separate the tweets from one another but it would seem that \\r\\n09/19/14 isn't an appropriate split string? Here is the code:

String[] value = line.split("\r\n09/19/14");

PrintWriter writer = new PrintWriter("hello.txt", "UTF-8");
writer.println(value[0]);
writer.close();

The text file 'hello', when I open it is just the following string again, "TweetJSONObject\\r\\n09/19/14TweetJSONObject". Any ideas as to where I'm going wrong?

Answer 1

You need to escape the backslashes:

String[] value = line.split("\\\\r\\\\n09/19/14");

---

Why so many backslashes?

In literal Java strings the backslash is an escape character. The literal string "\\\\" is a single backslash. In regular expressions, the backslash is also an escape character. The regular expression \\\\ matches a single backslash. So this regular expression as a Java string, becomes "\\\\\\\\" .

Answer 2

I would recommend using the library method Pattern.quote instead of trying to escape stuff on your own (which is too confusing and error prone). A small runnable example:

package net.sanjayts;

import java.util.regex.Pattern;

public class RegexTest {
    public static void main(String[] args) {
        String s = "TweetJSONObject\r\n09/19/14TweetJSONObject";
        String[] parts = s.split(Pattern.quote("\r\n09/19/14"));
        System.out.println(parts[0] + " --- " + parts[1]);
    }
}

//Output: TweetJSONObject --- TweetJSONObject

Answer 3

You need to escape the slashes

String[] value = line.split("\\\\r\\\\n09/19/14");

PrintWriter writer = new PrintWriter("hello.txt", "UTF-8");
writer.println(value[0]);
writer.close();